1. Field of the Invention
The present invention relates to a display device having an image acquisition function.
2. Related Background Art
A liquid crystal display is typically comprised of an array substrate having signal lines, scanning lines and pixel TFTs arranged in matrix, and a drive circuit for driving the signal lines and the scanning lines. With an integrated circuit technology drastically advanced in recent years, a processing technology forming a part of the driving circuits on the array substrate has been put into practical use. Thanks to the technology, it became possible to downsize and lighten the entire liquid crystal display. Such kind of liquid crystal display is widely used as a display device of various portable equipments such as a portable phone and a notebook PC.
There is proposed a display device having image acquisition function, which has closely assembled area sensors (see Japanese Patent Laid-open Nos. 292276/2001 and 339640/2001).
In this prior art display device having an image acquisition function, the amount of electric charge of the capacitor connected to the sensor is changed in accordance with the amount of light received by the sensor. The image acquisition is conducted by detecting voltages at both ends of the capacitor.
On the other hand, the liquid crystal display controls whether or not a light of a backlight source disposed in back surface passes through liquid crystal pixels to perform arbitrary display. At this time, if a lot of photoelectric conversion elements and circuits are integrated in the pixels, it is impossible to ensure sufficient aperture rate, and to obtain required display luminance.
The luminance of the backlight may be able to raise by some way, but this may, in turn, adversely increase power consumption. In the ordinary display device, it is difficult to provide the pixel with the photoelectric element and the circuit for more than bit. Because of this, unlike a CMOS image sensor and a CCD used for a digital camera and so on, the display device is able to directly produce only 1 bit of image pickup data. In order to convert this data into multi gradation data, it is necessary to perform specific processing in which a lot of image pickup processings are repeated while changing image pickup conditions, and addition/averaging processing is performed at outside. After the gradational differentiation, it is necessary to conduct general image processings such as gradation correction and defective correction conducted by the ordinary digital camera.
Although a dedicated image processing IC may be provided to conduct these processings, it leads to an increase in the manufacturing cost.